<p><it>Abstract</it>—In this paper we study the issue of integrity constraints in the <it>Information Source Tracking (IST)</it> method. The IST method is an approach to the management of uncertain data in database systems. The main idea behind IST is that database information is supplied, or confirmed, by information sources. The accuracy of data is modeled by the reliability of the contributing information sources.</p><p>In practice, information sources that are generally quite reliable may supply conflicting data at times. A database system based on IST must accept such data, and be capable of functioning correctly despite the inconsistency. We concentrate on cases where conflicting data is in violation of “key constraints, a special form of functional dependencies resulting from the imposition of a key for each relation in the database. We present an approach, based on the <it>adjustment</it> of conflicting information source reliabilities, to handle data in violation of key constraints.</p>